A voltage divider on the input will work fine. How about 5K from the input pin to GND and 7.5K from the input pin to your 12V source. If you need a little noise
immunity, you can add a .1uF cap across the 5K resistor.
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Re: How would you do this?
A voltage divider on the input will work fine. How about 5K from the input pin to GND and 7.5K from the input pin to your 12V source. If you need a little noise
immunity, you can add a .1uF cap across the 5K resistor.
Charles Linquist
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Re: How would you do this?
I would suggest optocoupler as TLP504 or similar.
Al.
All progress began with an idea
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Re: How would you do this?
Hi Al,Originally Posted by aratti
Just out of curiosity, why would you use the optocoupler?
Tony
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Re: How would you do this?
With optocoupler you will obtain Total isolation from the 5 volts rail and total immunity to noise.
Cheers
Al.
All progress began with an idea
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Re: How would you do this?
Actually the picbasic pro manual shows under the serin command, you
can input 12 volts directly through a current limiting resistor. (22k in example)
But if you truly need a reliable trigger, without false triggers, I agree with aratti
and use optocoupler and caps.
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Re: How would you do this?
If the grounds are not isolated, can someone explain to me why an optocoupler is more reliable?
Charles Linquist
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Re: How would you do this?
If some kind of voltage spike comes along the circuits other than ground, less paths of that spike to the uP reduces chance of frying.
Don
Amgen
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Re: How would you do this?
I agree Charles. Isolated grounds would be best. But if thats not practical, than keeping circuit neighborhoods isolated would be next best. At least thats the way I understand it and have seen in practice.
Meaning of neighborhood. If you already know this than I apologize. One neighborhood would be the analog section. Another would be the digital. All neighborhoods should have their own ground that leads back to the point where power ground comes into the circuit. This point will have the lowest impeadance to power/earth ground. In other words, all neighborhoods share their ground at only one point. Doing this keeps noise created in one neighborhood from effecting another.
This does not work for all applications but using an optocoupler will keep this idea in place.
Also this idea relies on the use of the right capacitors in the right place. I still don't fully understand how caps fixed certain high speed trigger problems i had.
...maybe it was inductance or quantum interactions ... i don't know ???
Last edited by MikeWinston; - 13th September 2011 at 19:51.
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